1. Field of the Invention
The present invention relates to projection type display systems for use in projecting an enlarged image onto a display screen through a projection lens which is obtained by modulating a liquid crystal panel in accordance with video data. The present invention further relates to a small-sized, highly portable, projection type display system using a liquid crystal panel as a light modulator.
2. Related Technical Art
In a typical small-size, highly portable, projection type display system (e.g., a projection type display system using a liquid crystal panel as an optical modulator), the projection lens has its focal length adjusted either manually by using mechanical means or automatically by using an electric motor operated by a switch. This is done because the distance between the projection type display system and an associated display screen changes each time the display system location or position changes.
The focal length adjustment process is specifically described below with reference to FIG. 8. FIG. 8 illustrates a diagram of the structure of a focusing mechanism which is useful for adjusting the focal point of a projection lens using an electric motor which is operated by a switch.
If a focus adjustment switch 504 is depressed or otherwise activated, pulses having a width proportional to the length of time the switch is depressed, are generated by a motor drive signal generator 502. As a result, a projection lens drive motor 501 is activated by this signal and moves or drives a projection lens 505 for a length of time corresponding to the pulse width so that the projection lens 505 is moved toward a screen 507 to change its focal length.
If, instead, a focus adjustment switch 503 is depressed or otherwise activated, projection lens 505 is driven, in the same manner as described above, away from screen 507 to change the focal length.
Using the operations as described thus far, focus adjustment switches 503 and 504 are operated in order to move projection lens 505 and alter the distance between projection lens 505 and screen 507 to a value equal to the focal length of projection lens 505. As a result, light modulated by an optical modulation block 506 in accordance with input video signals is clearly projected onto screen 507 on an enlarged scale by projection lens 505. In FIG. 8, reference numeral 508 designates a power supply for the motor drive signal generator 502.
Since the focal adjustment is accomplished by depressing or activating focal adjustment switches 503 and 504, according to this background art, the switches are continuously depressed while observing the imaged focused on screen 507, until the focus is adjusted to be in the vicinity of an optimum focal adjustment point. After this, the projection lens forward focal adjustment switch 504 or the backward focal adjustment switch 503 are also depressed several times while observing the on screen image until the optimum focal point is finally reached. This causes problems in operating the system because this requires depressing operation switches 503 and 504 several times until the optimum focal point is set.
If a projection system user with poor visibility or visual acuity is adjusting the focal point, current systems find it difficult to obtain the optimum focal point because the user has to observe or adequately perceive details of the image focused on screen 507 during adjustment. Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.